19302-921-003 Thermostat Rubber - Overview. The 19302-921-003 Thermostat Rubber is a genuine OEM component vital to the cooling system of Honda marine engines. It functions as a sealing gasket for the thermostat, ensuring effective temperature control by preventing water leaks and maintaining proper water flow within the engine cooling system. This part supports the engine cooling system, keeping Honda marine engines running reliably and efficiently. It is engineered to meet exact factory dimens